Electrical apparatus



July 30, 1940.

R. OVERHOLT, J R

ELECTRICAL APPARATUS Filed Sept. 8, 1939.

B Ik

SPI

Ema

lal E Figa y INVENTOR 6.2 mgm az/mazf.

HIS ATTORNEY Patented July 3o, 1940 UNITED STATES PATENT OFFICE 33 Claims.

My invention `relates to electrical apparatus and more particularly, to apparatus for providing a constant check that a normally inactive circuit or one carrying only a small current is continuous and contains no defects such as would render the circuit inoperative at a time when the circuit is called upon to function'and to carry a relatively much larger current. My invention is` also directed to means for causing the current supplied to a load to take a given path as long as the load current is at or below a predetermined value,and automatically and abruptly to take a different path when the 'current exceeds such predetermined value.

More specifically stated, my invention provides the electrical equivalent of a mechanical by-pass valve whereby uplto a certain point, the valve remains closed and the flow is confined to a given channel but when the ow increases above this point, the valve opens suddenly and automatically by-passes the excess flow. Looking at the invention from 'still another viewpoint, the apparatus may be considered as an automatic switch without moving parts which, of its own accord, makes available a high current shunt path when the load increases above a predetermined value. The apparatus embodying my invention is therefore capable of automatically and reliably distinguishing between a light and a heavy load at a location which may be removed from the point at which the load is applied and provides the sensitivity which is inherent in apparatus designed for low current operation while at the same time retaining the low impedance characteristics which are necessary for carrying substantial amounts ofcurrent without undue voltage drop or excessive power loss.

One application in which my invention has special utility is in connection with track circuits for miniature or model railways for indicating the presence of a train on the track circuit.-

Another application in connection with the transmission of intelligence, such as telephone transmission, over an available power or communication circuit. It will be in connection with these specific applications that I shall describe my invention in order that its features and advantages may become more fully apparent. It will be apparent, however, that such description in connection with a model railroad track circuit or power line channel is presented by Way of illustration only and is not intended to limit the scope of the invention which is broadly useful in connection with any electrical supply circuit in which diversion of current to a second path is desirable when the current exceeds a predetermined value,

I shall describe several forms of apparatus embodying my invention, and shall then point 5 out the novel features thereof in claims. l

Fig; 1 of the accompanyingdrawing is a diagrammatic view showing one form of apparatus embodying my invention, as applied to a model railroad trackcircuit. Figs. 2, 4, and 5 are dia- 10 grammatic views also embodying my invention and showing modified forms of the apparatus of Fig. 1. Fig. 3 is a diagrammatic viewembodying my invention in which the invention is used to provide communication over an existing load cir- 15 cuit.

Similar reference characters refer tb similar parts in each of the several views.

One difliculty in providing a simple and re-` liabletrack circuit for a model railroad is caused by the relatively high resistance of lthe train shunt due to the light weight of the rolling stock. If` the signaling current is obtained from the rails which also carry the propulsion current, then a further diillculty arises due to the fact that ordinarily the propulsion current must be of different character from Athe track circuit current in order that the track relay will not be falsely energized by the propulsion current with a train occupying the block. Moreover, even if the propulsion current is direct, the signaling current being alternating, there is still some possibility of false energization of the signaling apparatus due to the effect of pulsations or impulses in the .propulsion current. All of these `diilculties are overcome in a simple and eective manner in the apparatus embodying my invention. That is to say, the track relay responds positively to the application of a model railroad train shunt even though the shunt is of very high 0 resistance, and remains definitely unresponsive when the track is unoccupied. Moreover, the propulsion current-in the apparatus embodying my invention need not necessarily be of different character from the track circuit current but may 4f be furnished either from a battery, a transformer, or other suitable source similar to that which energizes the track relay. Furthermore, any suitable number of track circuits may be energized from a single propulsion battery and a single track circuit battery, or from a single transformer, aswill appear hereinafter. Accordingly, the apparatus embodying my invention not only eliminates the necessity for a third rail to carry the propulsion current as the usual two 55- rails sumce for carrying both the propulsion and track circuit energy but lit also eliminates the added cost and maintenance involved in the use `of individual batteries or transformers for each track circuit section. The foregoing features and advantages will be best understood from a description of the apparatus and operation of an illustrative track circuit such as that shown in Fig. 1 of the drawing.

Referring to Fig. 1, the reference characters I and Ia, designate the, two rails of ya stretch of track which is divided into track circuit sections by means of the insulated rail joints 2. Only two track circuit sections ar'e shown in the draw@ ing. The rails I and Ia may, of course, represent the supply conductors of any suitable electrical or transmission circuit across which may be connected any suitable load R. As shown, the. load R represents the shunt resistance load of a model railroad train as the train proceeds over the track section.

Across the rails I and AIa is connected a battery or other suitable source of unidirectional current A, through an asymmetric unit K. Source A is the propulsion battery which yenergizes the train load R. The asymmetric unit K is so 4poled-with respect to the battery A that a low resistance path rfor the ow of propulsion current is provided which path maybeftraced as follows: starting from the positive terminal o f battery A, through wire 3, rail I, load R, rail la, wire t, asymmetric unit K, and wire 'I, to the negative terminal of battery A. The asymmetric unit K may conveniently be a'dry disc copper oxide rectifier such, for example, as disclosed in Letters Patent of the'United States No. 1,640,335,

granted to Lars vO. Grondahl on August 23, 1927. On account of the high ratio of resistance in the reverse current direction ascompared with the resistancein the forward current direction in the copper oxide rectier, vI have found this rectifier to be particularlyv effective in providing the desiredoperation.y It will be obvious, however, that any suitable 4asymmetric unit having an appreciable resistance ratio as well as a suitable current-carrying capacity may also be used- Across the terminals ,5-6 of the asymmetricV unit K is connected a second source of unidirectional current B, in series with `a relay D. The relay D may perform any of the usual functions `of a track relay such as controlling signals or other signaling or control apparatus over its contacts 8-9 8--I'IL The particular circuits and apparatus controlled b y relay D form no part of my invention and since these are well known,

theyliave not' been illustrated in the drawing inl order to simplify the disclosure. Onecircuit for relay D (which however does not pick upthe Y relay unless the section' is occupied, as described'V 60 hereinafter) may be traced from the positive terminalof battery B, wire 1, asymmetric'unit K in Athe reverse or high resistance direction, wires I2. and II, and winding of relay D, to the 4negative terminal of battery B. If desired, the battery'B 65 may be eliminated and an equivalent voltage obtained from the propulsion battery A by connect- 1 to a suitable tap on this.

i ing the conductor battery.

With the'track section E--F unoccupied '(no 70 load connected across the supply conductors I and Ia) no propulsion current will` .flow through the unit K in the forward direction and the only current'in relay D 'will be that supplied by battery B through unit K in the high resistance 75 direction. The apparatus is so proportioned that D, and not any will pass through -thislcurrent is insufficient to cause the relay to aid in supplying a certain amount of lcurrent to relay D over a circuit passing from the positive terminal of battery A, through wire 3, rail I, load R, rail ia, wires i and II, winding of relay D, through the battery B,I to the negative terminal of battery A. The relay D may or may not pick up, depending upon whether the load resistance R is below or above the predetermined value, as established by the voltage of battery A and the remaining constants of the apparatus. Entry of a train will, of course, pick up the relay because the resistance of the load R under thiscondition will be -below the predetermined value.

As the load resistance R decreases below the predetermined value, relay D will pick up and will remain picked up thereafter without becoming-'substantially overenergized, even though the load resistance should continue to decrease further and reach a very low value. That is to say, up to a certain point, all of .the current will flow through the circuit which includes relay D, and no current will flow' through the rectifier K in the forward orv low resistance direction. Suddenly, however, as a critical point in the load current is reached, any further increase in the load current will causecurrentto begin to be by-passed through the rectier in the forward or low resistance direction so that very 1ittle,'if any, of the additional current will iiow through relay D. This operation may be explainedv by stating that the apparatus behaves as though the circuit of relay D were capable of accepting only a predetermined amount of current, up to its saturation point, but when this point is reached and the circuit is lledf substantially all ofthe additional current will be by-passed automatically over the low resistance shunt path including rectifier K. The "action` of the rectifier K in bypassing. -the additional current due to increased load will not D to any appreciable extent so that relay D will remain energizedgcontinuously during the time that the track section is occupied or an appreciable load R is effective. When the load R is decreased, the forward current through rectier K will also decrease but no substantial change in current through relay D will occur until the forward current reaches -ing a marked decrease in the current traversing relay D and a release of this relay. Accordingly, when the train yacates the section E -F and the loaii current drops to zero, relayD will release.

One wayin which the foregoing operation may be more clearly understood is to assume, for purposes of explanation only, that the asymmetric unit Kis a perfect valve, having infinite resistance in the reverse direction and zero resistance in the forward direction. With such an asymmetric Iunit, it will be apparent that starting at extremely high values of load resistance, all of the current from battery A will go through relay the rectifier. Under this condition, practically the full voltage of battery B will be eifective across the rectifier a'ect the current flowing in relay vci:

. v 2,209,845 K and will be in the reverse or opposed direction tential will be that of the battery' minus the small relay-drop. Accordingly, no currentfrom battery A will flow throughA the rectier and all of the current will iiow through relay D.

As the load resistance is decreased in small steps, the current in relay D and the voltage drop in this relay will progressively increase, thus causing` the reverse potential across the rectifier K ,to decrease progressively. At some point, the current through relay D will be sufflcient to cause the relay to pick up, but at this point the drop across relay D will still be less 'than the voltage of battery yB so that a certain reverse potential will still renain across the rectiiier and the rectifier will still pass no current (remembering that a perfect valve has been assumed) Finally, at a critical value of the load resist ance, the voltage drop across relay D will just equal the voltage of battery B so that the potential across the rectifier will become zero. This 'value for relay marks the transition point in the rectifier characteristic and under the assumed condition of zero resistance in the forward direction, it is obvious that at and beyond this point, all of the increase in current from battery A will pass lthrough the rectifier,

relay .D remaining energized under this condition. y

Considering now anactual asymmetric unit having the usual properties which render it a somewhat imperfect valve, the same general operation as discussed above'will be obtained, the

only' diserence being that the transition point.

will be less sharply defined and that some current will ow in relay D from' battery B even before any load is applied to the circuit I-I a. Also, the energization of the relay D will increase slightly after the transition point ris reached, due to the voltage drop across the rectier K in the forward direction.

. It is desirable toproportion the apparatus in such a manner that relay D will pick up at a current value substantially below that which the relay receives at the time the rectifier passes through its transition point and begins to by-pass the excess current. Otherwise, should the relay be designed to pick up just at the transition point,

a failure to pick up might occur in the ,event that the voltage of battery B dropped below its normal value. This is because a drop in voltage of battery B causes the transition to occur at a lower value of load current and the pick-up current D might never be reached underl this condition. v- A I have found in practice, for example, that with a battery B of 4 volts, a resistance for relay D of 125 ohms and a pick-up current of about 20 milliamperes, the maximum current which pa'sses' through relay D is about 50 milliamperes', all current in excess of this value and amounting to several amperes being by-passed through the rectiiier. These values are, of course, merely illustrative and are .not intended as limiting the proportions of the apparatus because, obviously, the vapparatus is broadly useful independently of the magnitude of the current or its particular division ratio. As pointed out above, an appreciable spread battery"l between th'e pick-up current and the maximum current in relay D is desirable for practical reasons in order to take care of certain factors such as batteryvoltage drop, lead drop, change in resistance of relay D with temperature, etc. It will also be understood that the relay D is not essential for establishing the desired current division,

provided that the resistance in the portion of the circuit which includes wire Il and battery B is sumcient to.. produce the necessary voltage drop as load current flows therein to reduce or eliminate the reverse voltage drop across the rectier K.

l The shunting sensitivity of the apparatus in Fig.

`1 is controlledI largely by the voltage of battery A.

Doubling the voltage of this battery will approximately double the value of the resistance R effective for bringing about the transition in the rectifier characteristic. That is,-if the battery B, rectifier K and relay D are once determined, then the load current alone will determine the transition point. An increase in the voltage of battery A will therefore permit a, corresponding increase in the load resistance which is effective at the time when relay D operates. An increase in the voltage of battery B, on the other hand, increases the current sensitivity of the circuit in that it permits a high resistance, low current relay to be used. Too great an increase in the voltage of battery B is undesirable, however, because it tends to increase the reverse currentthrough the rectier. A practical limit is reached when the current sensitivity of the apparatus becomes so 'f high that the reverse current through the rectifier will not permit proper release of the relay under a condition approaching no load across the rails. i

It will be noted that the batteries A and B provide the propulsion and track circuit currents, respectively, not only for section E-F but also for section F-G and for as many additional sections of track (not shown) as may be desired. The operation of the apparatus for section F-G when a train enters this section is identical with that described for section E--F and will be understood without further detailed explanation. The presence of a trainl in one or more track circuits will not affect the apparatus in the remaining track circuits provided that the batteries A and B are chosen to -have suflicient capacity so as to maintain their voltage substantially" constant under lthe various load requirements of the apparatus.

f gized when the'section is unoccupied and alternating track circuit current is used for signaling purposes. 'I'his current is supplied from an alternating current generator G connected across the rails through a pair of suitable blocking condensers C which prevent the now of propulsion current from source Ain the Vcircuit of generator G and which prevent the rails of adioiningsec-v tions from being connected together electrically over the generator connections. Energyfrom the generator -is normally supplied to the primary vwinding I3 of a transformer T, through the batteries A and B in series. 'Ihe output from transformer T is delivered by winding I4 to the nor' mally energized track relay DI, through the fullwave rectifier K2 which is connected in the usual manner.

Assuming that no train occupies the section EI-Fl, alternatingv current from generator G will iiow in winding I3, thus causing relay DI to this condition, the rectifier d remain energized. Winding i3 is designed to have an appreciable vresistance but'the peak value of the impulses of current and necessary for maintaining relay DI energized is insumcient to eliminate the reverse potential drop which exists across the rectifier Ki due to the battery B when the section is unoccupied or the circuit is Votherwise Without `l Under KI is incapable of passing any current in the' forward or low resistance direction.

Assuming next that a very light load is connected across the track circuit, lthis load will cause a small current to be suppliedover a circuit which may be traced from battery A, through wire 3, rail I, load R, rail la, wire ii, winding I3, and battery B, back to battery A. This current will cause a voltage drop in the resistance of winding i3 which will decrease the reverse voltage drop across the rectifier Kl. A further increase inload will cause the reverse voltage drop across the rectifier to decrease still further until at acertain critical load,

this drop will becomezero and any further increase in load current from battery A willthereafter be by-passed through the rectier.

When the rectifier voltage drop becomes exactly zero, considering only the effect of the batteries A and B,`the rectifier KI will provide substantially half-wave rectification with respect to the current from generator G because all of the current impulses of normal polarity will be by-passed through the rectifier in the forward.l direction,

the remaining current in winding i3 being half- Wave pulsating current of reverse instantaneous polarity. Ii desired., relay DI may be designed so `that it will release under the above condition of load, as represented by half-wave current in winding I3. This condition. may, for example, represent the maximum resistance train shunt which itis desired to detectjby means of the apparatus.

If the' load is increased still further, the rectifier voltage drop willbecome increasingly positive and will cause the pulsating current in winding I3 to decrease correspondingly. At some value of the load resistance, the positive voltage drop across the rectifier due to batteries `A and B will be just sufiicient to balance the peak` value of the pulsating potential from generator'G existing across winding I3 so that beyond this point, substantially all of Athe current will be by-passed bythe rectifier KI and practically no .current from generator G will ow in winding I3. It is -very clear, therefore, that the apparatus may be so designed and proportioned as to be highly sensitive to the entry of a train into Athe section or the presence of a comparatively light load across the conductors `I' and la.

The presence ofthe condensers C in the generator circuit provides an additionaladvantagev` in that when a load is.- applied across the rails,

the impedance of these condensers causes a drop in inter-rail potential which further aids the release of relay- DI. From the foregoing, it is apparent that my in' vention vcan readily be applied to alternating current track circuits employing direct current propulsion energy (as well as alternating current propulsion energy as will appear hereinafter) and that 'the apparatus embodies a high degree of senstitivity' to the presence of av train. shunt or other light load connected across the rails or conductors. It should also be pointed out that, if. desired, the batteries 7A and B can be replaced by the output terminals of suitable substantially flowing in -this winding transmitting location. -.-proportioned that at no load or at light loads,

there will alwaysbe'present-at least'a -small nega- .50 'tivefvoltage drop constant-potential rectiiiers alternating current source. The batteries A and B may be used to energize additional track sections such as `liI-GI, 'as in Figi. Only a portion of the apparatus associated with the latter section is shown in the drawing, it being understood that the transformer Ta. energizes a rectifier and relay similar to the corresponding appa-` ratus associated with section El--FI Referring now to Fig. 3, the apparatus of this 10 figure is generally similar to that of Figs. 1 and 2 except that instead of using atrack circuitand a track relay or other superimposed a communication channel on the load conductors in the form of a telephone circuit 15 which is available at all times when the load on the conductors is at or below a given value, for transmitting speech or other intelligence along the conductors in a simple, direct and inexpensive manner.

The transmitter TR at the first location superimposes ductors 2I-22, through the medium of windings I5 and i6 of transformer TI, and condenser Cl.

Battery BI is .thesource of energy for the voice transmission. The details of this transmitting v and receiving (or speaking) apparatus have not been shown, as this apparatus is well known and,

of itself, forms 'no part of mypresent invention.

This transmitting .apparatus corresponds generally with the generator G of Fig. 2. Similarly, the load L which may at times' be connected across the conductors 2I-22 by means of the switch S corresponds generally with the load R of Figs. 1 and 2. The remaining apparat which 35 is connected with the conductors 2l an 22 by means of wires which has been described in considerable detail.

Since the essentialoperation is the same in both 40 Figs. Zand 3, it will be unnecessary to repeat this operation other thanlto point out the differences therein.

When there is no load on the conductors 2I-22,- rectifier K3 passes no current in the for- 45 are transmitted by' way of winding I1, through 55 the two conductors 2 I-22,and winding l 6, to the' receiving winding 20 of the speaker SP atthe first The apparatus may be so across thev rectier K3 during transmission so that under this condition no appreciable distortion of the speech willv occur.

If the load is increased to a point v such'that the rectier potential drop approaches zero or 65 swings positive during transmission, a certainamount of distortionwill o ccur due tothe rectifying action of the rectitlerKB `whichwill partly suppress impulses of one polarity in winding I1. v`1f the load is sufciently large,.these impulses 'l0 may become :ompletely suppressed 4and the s uppression may also be partly vor wholly effective with respect to impulses of 'the other polarity.

Under the latter condition, speech transmission may no longer be possible. Howevcr,'by using 7 5 energized from an signaling device, Ihave voice frequency currents upon the con- 3 and l is similar to the correspending apparatus of Fig. 2, the operation of which reproduces the code instead of telephone transmission, greater distortion is permissible so that the operating range of the apparatus may be increased in this manner. Accordingly, it will be apparent that I have shown in Fig. 3 a system which is capable i of providing satisfactory two-way communication in a simple and inexpensive manner, up to a given value of load.- over the same pair of conductors which are atqtimes used for supplying power or are used for other purposes.

Referring now to Fig. 4, the apparatus shown in this figure is very much like that of Fig. 1 with the exception that relay D2 is of the'normally energized type, asV in Fig. 2, and is polarized with its-armature biased to its neutral position. Normally, when the section E2F2 is unoccupied the relay D2 is maintained energized by the reverse voltage drop across the rectifier K4 due to the ow of current from the battery B through the resistor Rl and rectifier K4 in the reverse direction. Polar contact 24-25 will be closed under this condition. The resistor RI provides the initial reverse-voltage drop (which inFig. lis` provided by the resistance of the Winding of relay D) for opposing the ow of current from battery A through the rectifier K4 in the forward direction until the transition pointfis reached and the load R across the rails reaches a predetermined value.`

When a load is connected across the. rails orthe section E2-F2 becomes occupied, the reverse voltage drop will be reduced suiiiciently to cause the relay D2 to release, opening its contact 24-25 and closing its Contact 24-21. At ak critical value of load, the net current through the recti- Iier will be zero, and any further increase in the ytermined load R,

load will cause current to iiow through the rectier in,the normal or forward direction, thus establishing a forward voltage drop across the rectifierl y Relay D2 and the remaining apparatus are so designed and proportioned that the reverse voltage across the` rectifier K4 with the sectionl E2-F2 unoccupied is sufficient tol maintain'the contact 24-25 closed.' The resistance of relay D2 should be sufficiently high so as not to mask the rectier characteristics in order not to reduce the sensitivity of the apparatus. At a given value of -the load current corresponding to a predethe reverse voltage drop across the rectifier K4 will be insuiiicient -to maintain relay D] energized so that its polar contact 24-25 will be opened. Any suitable indication or control circuits for governing4 signaling or other ape paratus may be controlled over th'e contacts 24-25 and 24-21 of relay D2.

When the section E12-F2 is occupied, the ioad l current will ordinarilybe suiiicient to cause the voltage drop across the rectifier to reverse and become positive: 'I'his voltage drop will not be very'high because of the-relatively low resistance lof the rectifier. K4 in the forward 'direction, but may be .enough to cause the armature of relay D2 to swing Ato the left, closing contact 24'-26. If desired, contacts 26 and'2l2 may be connected together so that the closing of either pied indication.

, The circuit of Fig. 4 incorporates a nuxnber of safety features in that any failure such as an open circuit in the winding of relay D2, a shortcircuitinrectier K4, a failure of the battery B,

or anqopen circuit/in vthe resistor RI will each cation of a fault in the circuit.

.or the two conductors ior example, be suitable for l ratus for section 'Ef-F.

Referring now. to Fig. v5,1 have shown in this figure the alternating current equivalent of the apparatus of Fig. 1. The transformer T3 has its input windingienergized from a suitable source of alternating current and has its output winding divided into twoportions 28 and 29 which correspond respectively to the sources A and B of Fig. l. The connections of these windings with the rectifier K5, relay D3 and rails l-la of the track circuit are identical with the connections of the batteries A and B in Fig. ll and so need not be described 'in detail. In operation. with the section "unoccupied, relay gized because the potential of winding 29 is insuiiicient to pick up this relay over the rectier circuit. 'At a predetermined value of the load R, relay D3 will pick up and will remain picked up thereafter as the load is increased still further. The unidirectional current in relay D3 has been found upon test to reach a saturation point, Jas in Fig. 1, so thatthe path through the recti- :lieved unnecessary for an understanding of the invention to present a theoretical analysis of the operation.

The apparatus of Fig. 5 provides an operation D3 will be deener- The complete theory apparently unwhich, though not so sharply defined as in the direct current apparatus, is generally similar to that provided by the battery operated systems.

For example, using a 60 cycle transformer deliveringa constant voltage of 6 volts from its winding 29 and 8,-8 volts from its winding 28'; a direct current relay D3 Wound to a resistance of 125 v ohms and having a pick-up of '7 milliamperes as read on a direct current galvanometer type milliammeter; and a half-wave rectiiler K5 built up of the usual copper oxide discs, the relay current was observed to increase `gradually as the lloadresistance was decreased, reaching a saturation value of'about 18 milliamperes at a load current of about milliamperes as read on direct current galvanometer type meters. Beyond vthis point, no increase in the relay current was observed even though the load current' was increasedto 500 milliamperes, thus showing that the apparatus of Fig. 5 which employs alternating current sources provides the same general type oil operation as the direct current apparatus of Fig. -1. The apparatus just described would, a model railroad employing alternating current for both propul- .sion and track circuit control.

It will be understood that the above specic values are given solely for the purpose of illustration in order to provide a more'clear understanding of the invention, and not in any limiting sense whatever because, obviously, the apparatus may be proportioned in many different ways-to provide the operation contemplated by the invention, depending on the particular service which the apparatus is to perform. When used in conjunction with model railroad operation, it will be understood that the single transformer T3 of Fig. 5 may be used for energizing additional track sections'such as F-G of Fig. 1 by adding a rectifler- KS'and relay D3 for eabh ad-v ditional trackycircuit sectionv and' 'connecting these with the remaining apparatus in the same manner that the corresponding rectifier Ka and relay Da of Fig. 1 are `connected with the appalfigures, it will be From the foregoing description of the several apparent that an important feature of my invention is the provision of apparatus which causes a first circuit to carry substantially all ofthe current up to a given predetermined value and then as the current is increased above this value, suddenly and automatically to cause the excess current to be switched or by-passed intol a second circuit, without employing any apparatus having moving parts for` performing this operation. Moreover,

- the apparatus embodying my invention makes. it

, lonly a few forms of apparatus embodying lloads exhibits possible to detectthe flow of very small cur,- rents by means of relatively rugged and reliable apparatus which. in itself is not required to ,be ultra-sensitive. While the current is being detected (in the low current range) the voltage effective across the load terminals exhibits all the characteristics of being fed from a s'ource havuseful functions, as Well. The apparatus may also be energized from alternating current sources and although the operation is-not quite so sharp-- ly dened in such apparatus as in the systems` the im` which employ direct current* sources, portant advantages of the apparatus are available in both. Obviously, these general features' of operation are capable of being used advantageously in many practical applications, those described. herein being chosen merely for the purpose "/of setting forth more clearly certain fundamental aspects of the invention, rather than in any limiting sense.

Although I have herein hown and described my i11- vention, it is understood that various changes and modications may be made therein within the scope of the appended claims without de#- sarting from the spirit andpscope of my invenion. f

.Havingthus described my claim is: A Y

l. In combination, a pair of conductors, a main source of unidirectional current, an asymmetric invenucn, what i unit, means including said asymmetric unit for direction to aid the vflow of current -being poled in a direction connecting said mainysource across said conductors, said asymmetric unit being poled in a from said main source, an auxiliary source of unidirectional current, .an impedance, means including said impedance for connecting said auxiliary source across said asymmetric unit, s'aid auxiliary source to oppose the iiowA of current 'from said main source \v through said asymmetric unit, and a load connected across said .conductors and energized, from said main source, said impedance having a relatively low` value as compared with the resistance of said asymmetric unit in the reverse-current direction, the potential'. of said auxiliary source being. so` chosen with respect to the voltage drop caused by the ilow of current to said lo'ad through said simple signaling channel over an conductors ontrack Vrails and may be usedto perform many other impedance that at a predetermined value of said load current said auxiliary source potential and said voltage drop will substantially neutral'- ize, whereby upon a lfurther increase in the load current the asymmetric unit will by-pass the portion of said load current above said predetermined value around said impedance.

2. In combination, a pair of conductors, a load connected across said conductors, a main source of unidirection current, an asymmetric unit,.y

means including said asymmetric unit for connecting said main source across said conductors, said asymmetric unit being poled in a direction to aid the flow of current from said main source to said load, an auxiliary source of unidirectional current, an impedance, and means including said impedance for connecting said ,auxiliary source across said asymmetric unit, said auxiliarysource being poled in a direction to oppose the ow of current from said main source through said asymmetric unit, the parts being so proportioned that at a predetermined value of load current, the voltage drop in said impedance due /to the now of saidload current Will substantially neutralize the potential'of said auxiliary source,

. thereby permitting any further increase in the load current to be by-passed around said 'impedance through said asymmetric unit in its vforward direction.

3. In combination, a first circuit comprising a main source of unidirectional current, a load, and an asymmetric unit poled in the direction to aid the iiow of current from said main source to said load; a second circuit comprising an auxiliary source of unidirectional current, said main source, said load, and an impedance, said two sources lbeing connected in series-aiding relation; and a third circuit comprising said auxiliary source, said impedance, and said asymmetric unit poled in a direction to oppose the flow of current from said auxiliary source to said impedance; the parts being so proportioned that at ai-pr'edetermined value of current. through said load, the resultant potential drop across said asymmetric unit will be substantially naero, whereby an increase in-current through said load above said predetermined value will cause current to be by-passed around said impedancey through said asymmetric unit.

4. Current diverting apparatus comprising, in combination a iirst circuit including a lmain source of unidirectional current, a load,` andan asymmetric unit poled invthe aiding .direction with respect to said main source; a second circuit .including an auxiliary source of unidirecftional current and said main source connected in series-aiding relation, `said load, and an imy pedance; anda third circuit including said auxiliary source, 'said impedance, and said asymmetric unit connected inits blocking direction; 5. Current diverting apparatus comprising, in combination, a rst circuit including a vmain source of current, a load, and an asymmetric unit; a second circuit including an. auxiliary source of current and saidmain source corn'rectedv i inseries-aiding relation, said, load, and an' impedance; and a third circuit including said auxiliary source, said impedance, and said asymf metric unit, the parts being so proportioned that /I/ above a predetermined value of said, load sub/ stantiauy au .onine 10aa current wm be byl passed around said impedance through said- A asymmetric unit. 6. Apparatus for preventingthe current in a given circuit from exceeding a `predetermined 2,209,845 y value comprising, in combination, a main source of unidirectional current, an auxiliary source oi unidirectional current connected in series-aiding relation with said' main source. a load impedance and a bias impedance connected in series with each other and in a series circuit with said two sources, said bias impedanceiaving one terminal connected with said auxiliary source, and an asymmetric unit connected 'between the junction Apoints of `said two impedances and said two sources and ypoled in a direction to aid the ow of current .from said load impede-nce'.

7. Apparatus for given circuit from value comprising,

main source through said preventing the current in a exceeding a predetermined in combination, a main source of current, an auxiliary source of current c0n,

nected in series-aiding relation with said main source, a load impedance and a bias impedance connected in series with each other and in a seriescircuit with said two sources, said bias impedance having one terminal connected with said auxiliary source, and an asymmetric unit con- ,nected between the junction points of said two impedances and said two sources, the parts being so `proportioned that below a predeterminedvalue of said load impedance substantially all of the load current will be by-passedaround said bias impedance through said asymmetric unit.

8. In combinatioma of conductors, a load, an asymmetric unit, means for supplying unidirectional current over said conductors to said load through said asymmetric unit in its aiding direction, an impedance traversed by a portion of the current supplied to said load, and means including ten'tialv drop across said asymmetric unit in a direction load at all values of said load below a given predetermined value, whereby substantially all of said load current will traverse said impedance below said predetermined value and whereby an `increase in said load above said predetermined value will cause the excess current to be bypassed around said impedance through said asymmetric unit. Y

9. In combination, a pair of conductors, a'load,

an asymmetric unit, means ,including a source of unidirectional current for supplying current toA said load over said conductors through said asymmetric unit poled in the aiding direction with respect to saidvsource, an auxiliary circuit excluding/said asymmetric unit and supplying current from said main source to said load, and means included in said auxiliary circuit for establishing a potentialA drop across said asymmetric unit in a direction to oppose the ow of current to said load through said asymmetric unit at all values of'said load below` a given predetermined value, whereby substantially all of said load current will traverse said auxiliary circuit belowsaid predetermined value and whereby an increase in said load above said predetermined value will Vcause the excess current to be by-passed around said auxiliary circuit through said asymmetricunit.

10.' An automaticswitching device for causing` currentl tobe by-passed from one into another circuit when the current exceeds a predetermined value, all of the component parts of said device being stationary'comprising, in combination; a rst circuit including a source of unidirectional current, a load, and an asymmetric unit poled in the aiding direction with respect to said source; a second circuit including said source and said said impedance for establishing a poto oppose the flow of current to said and also in a series I connected from the load but excluding said asymmetric unit; and means included in said second circuit for establishing a potential drop across said asymmetric unit in a direction to op'pose the :tlow roi current (to said load through saifd asymmetric unit at all values of said load current below said predetermined value, thus confining said load current to said second circuit until said predetermined value is exceeded, whereupon the excess current is Icy-passed through said asymmetric unit into said rst circuit.

11.1n combination, a pair of conductors, a main source of unidirectional current and an asymmetric unit poled in the aiding direction with respect t said main source and connected in series across said conductors, a load connected across said conductors, an auxiliary source of unidirectional current connected across said asymmetric unit in a direction to oppose the flow of current'from said main source to said load through said asymmetric unit, and an indicator connected in series with said auxiliary source across said asymmetric unit for indicating when the current supplied to said load exceeds a predetermined value and for causing a potential drop due tothe load current passing therethrough which opposes the voltage of said auxiliary source to thereby aid the iiow of an increased load current through said asymmetric 12. Apparatus for indicating the integrity of a circuit comprising, in combination with a pair of conductors adapted to supply current to a load, a main source ofunidirectional current and an asymmetric unit all included in said, circuit, an auxiliary source of unidirectional current connected across said asymmetric unit in a direction to oppose the flow of` current from said main source in said circuit, and an indicator connected in series with ysaid auxiliary source across said asymmetric unit. r

13. Apparatus for indicating the integraty of a circuit comprising, in combination with a pair of conductors adapted to supply current to a load, a main source of current and an asymmetric unit all included in said circuit, an auxiliary source of current connected across said asymmetric unit l'in a direction to oppose the flow of current from said main source in said circuit, and an indicator connected in series with said auxiliary source across said asymmetric unit.

14. In combination, a iirst circuit comprising a main source of unidirectional current, a `load, and an asymmetric unit poled in the aiding direction with respect to said main source; a second circuit comprising an auxiliary source of uni` nected in series-aiding relationship, said load,

and a control relay; and a third circuit comprisving said auxiliary source, saidcontrol relay and poled in its blocking direcsaid asymmetric unit tion; and signaling apparatus governed by said control relay. x i

n 15. Means for preventing the current in a given circuit from exceeding am predetermined value comprising, in combination,\ a main source of unidirectional current, an auxiliaryfsource of unidirectional current connected in series-aidingi'elationship with sai main source, a control/relay and a load connec ed in series with each/other circuit with said two sources, said control relay having one terminal connected with said auxiliary source, an asymmetric unit other terminal ,of said control relay to the junction pointof said two sources leo and poled in a dierction to aid the iiow of current from said main source throughsaid load, and signaling apparatus governed by said control relay. l

16. Apparatus for detecting the presence of a relatively small current in a load conductor which at times carries a relatively heavy current comprising, in combination with said conductor, a source of unidirectional current, an asymmetric unit, a load; means for connecting said asymmetric unit in series with said source, said load, and-said conductor in a direction to aidthe flow 4of`load current from` said source through said conductor; andan auxiliary path in multiple with said asymmetric unit for the flow of current through said conductor, said auxiliary path including means for establishing a reverse potential drop therein for opposing the iiow of said load current through said asymmetric unit until the current in said auxiliary path reaches a predeterminedvalue.

at times carries. a relatively heavy current comprising, in combination with said conductor, a source of unidirectional current, an asymmetric unit, a load; means for connecting said asymmetric unit in series with said source, said load, and said conductor in a direction to aid the flow of loadcurrent from said source through said conductor; an auxiliary path in multiple vwith said asymmetric unit for the ow of current -through said conductor, said auxiliary path including means for establishing a reverse potential drop therein-for opposing the flow of said l'oad current through said asymmetric unit ,until the current in said auxiliary path reaches a predetermined value, and detecting means energizedI from thepotential drop across said'asym- -metric unit.

18. In combination with a section of railway track, a source of unidirectional current, an asymmetric unit, means for connecting said for detecting the presence of a` relatively small current in a load conductor which' the rails of said section 'through` said asymmetric unit poled in the aiding direcy tion with respect to said source for supplying current to said rails when the'section isoccupied, an auxiliary path isi multiple .with said asymmetric unit for alsov supplying current from said source to said rails when the section is 'l. occupied, and means included in said auxiliary path 'for establishing a reverse potential dr'op for opposing the flow of rail current through said asymmetric unit until the current in said aux-v liliary path reaches a\predetermind value.l

19. 1n combination with a; erst and a second section of railway track, @me source of unirlirec,v c o tional currentfor both said sections', a first and a 'second .asymmetric fonsaid rstand said means for-connecting said source across the rails of-each section tion and an appreciable propulsion potential drop -through the associated asymmetric unit poled in the aiding direction with spect'to said source for supplying current t6' the rails of the respective section when the section is occuped, an auxv iliary path in' multiple with each to the rails of the vrespective section when .the section is occupied, and means included in'each auxiliary ,path for establishing va reverse potential drop for opposing the ow of rail current through the respective asymmetric unit until the current in the associated. auxiliary pathreaches a prqedetermined yalu'e. o 2 0. In combination with a .rst and a second l ymriietric,` A unit for also supplying current fromA aid source y and a second asymmetric unit for said rst and said second section respectively, meansvfor connecting said jmain source across the rails 0f each section through the associated asymmetric unit poled in the aiding direction with respect to said mainsource for supplying current to the rails of the respective section when the section is occupied, one auxiliary source of unidirectional current for boths said sections, said auxiliary source being connected across each of said asymmetric units in'a direction to oppose the iioW of current from said main source to the rails through the respective asymmetric unit, land means associated with each asymmetric unit and connected in series with the asymmetric unit and said auxiliary source for causing a potential drop due to rail current from said main source passing therethrough which opposes the voltage of said auxiliary source to thereby aid the flow of` an increased rail /current through the associated asymmetric unit.

21. In combination with .a iirst and a second section ofrailway track, one main 'source of undirectional current for both said sections, a iirst and a sec'ond asymmetric unit for said first and said second section respectively, means for connectirig said main source across the rails of each section through the associated, asymmetric' unit poled in the aiding direction with respect to saidy main source for supplying current to the rails of the respective section when the section is occu` rent for bothsaid sections, said auxiliary source being connected vacross each of said asymmetric units ina direction tovoppose the flow of. current from said main source to the rails through the respective asymmetric unit, andan impedance associated withy each asymmetric unit and conthe aiding direction with respect to said source, `and an auxiliary path in multiple with said as'ymmetric unit for the ow of said propulsion current, said auxiliary pat u establishing a reverse potential drop therein for opposing the iiow of propulsion current through said asymmetric unit, said auxiliary path also including a control relay which is deenergized when said sectionis unoccupied and' no current from said' source ows in said becomes energized when a train enters saidsecdevelops across said control relay. to oppose the effect of said means and to aid the flow of propulsion current through said asymmetric unit, and signaling apparatus governedby said control relay. i y l '23. In combination with a section of 'railway track andI a rail vehicle load thereon, a source of unidirectional current, an asymmetric iunit,

means for connecting said source across the rails Atiple with. said asymmetric 'lary path lncludingfmeayns or said yfsc'ztion through said asymmetric unit poled in the aiding direction with respect to said to said rail vehicle load, an auxiliary path in mulcurrent from said source to saidload, said auxilfor establishing a re- '.pied,one auxiliary source of unidirectional curv 1504 including means for auxiuary path but which f' 7o` source to thereby supply current from said sourcev unit for the ow of l verse potential drop therein for opposing the ow of said load current through said asymmetric unitand a relay also included in said auxiliary path for indicating the presence ofthe rail vehicle upon said section.

24. In combination with a section of railway track and a rail vehicle load thereon, a source of unidirectional current, an asymmetric unit, means for connecting said source across the rails of said section through said asymmetric unit poled Yin the aiding direction with respect to said source to thereby supply current from said source to saidrail vehicleload, an auxiliarypath in multiple with said asymmetric unit for the iiow of current from said source to said load, said auxiliary path including means for establishing a. reverse potential drop therein for opposing the flow oi said load current through said asymmetric unit, and

' signaling means controlled by the current flowing in said auxiliary path.

' 25. In combination with a section of railway track and a rail vehicle load thereon, a main source of unidirectional current, an asymmetric unit, means for connecting said source across the rails of said section through said asymmetric unit poled in the aiding direction with respect to said main source to thereby supply current from said source to said rail vehicle load, an auxiliary source of unidirectional current, and a track re lay connected in a series circuit with said auxiliary source across said asymmetric unit, said auxiliary source being poled in al direction to oppose the flow of current from said main source through said asymmetric unit until the potential ydrop in said track relay due to the ovv'of said load current therein exceeds a predetermined value.

26. In combination with a'section or railway track and a rail vehicle load thereon, a main source of current, an asymmetric unit, means for connecting said source across the rails ci? said section through said asymmetric unit to thereby supply current from said sourceto said rail vehicle load, an auxiliary source of current, and a track relay connected in a series circuit with said auxiliary source across said asymmetric unit, said auxiliary source being poled in a direction to oppose the iioW oi current from said main source through said asymmetric unit.v

27. In combination with a section of railway track and a rail vehicleloacl thereon, a main source of unidirectional current, an asymmetric unit, means for connecting said source across the rails of said section through said asymmetric unit poled in the` aiding direction with respect to said main source to thereby supply current 'from saidl source to said rail vehicle load, an auxiliary source of unidirectional current, a resistor connected in a series circuit with said auxiliary source across said asymmetric unit, said auxiliary source being poled in a'direction to oppose the ow of current from said main source through Said asymmetric unit until the potential drop across said resistor due to the iiow of current from svaid main source therein exceeds a predetermined value, and a polarized checking relay energized from the potential drop across said asymmetric unit.

28. Apparatus for indicating the integrity of a ci.cuit comprising, in combination With a pair of conductors adapted to supply current to a load,

1 a main source of unidirectional current and an asymmetric unit all included in said circuit, an auxiliary source of unidirectional current connected across said asymmetric unit in a direction to oppose the iiowkof current from said mainy source in said circuit, a resistor included in the connection of said auxiliary source with .said asymmetric unit, and an indicator energized from the potential drop across said asymmetric unit.

29. In combination, a rst circuit comprising a main source of unidirectional current, a load, and an asymmetric unit poled in the aiding direction with respect to said main source; a second circuit comprising an auxiliary source of unidirectional current, a resistor, said load, and said main source, said two sources being connected in series-aiding relationship; a third circuit comn prising said auxiliary source, said resistor, and said asymmetric unit poled in its blocking direction; and a checking relay connected across said asymmetric unit.

30. In combination with a section of railway track and a rail vehicle load thereon, a source of unidirectional propulsion current, an asymmetric unit, means for connecting said asymmetric unit in series with said propulsion source across said I track in a direction to aid the flow of current from said source to said load, an auxiliary source oi unidirectional current connected across said asymmetric unit in a direction to oppose the iow of current from said propulsion source through said asymmetric unit, a source of periodic current connected across said track, and signaling apparatus connected in series with said auxiliary source across said asymmetric unit and responsive to the iiow of current from said periodic metric unit in series with said source across said conductors in a direction to aid the oW of current from saidsource to said load, a transformer, an auxiliary path in multiple with said asymmetric unit including said transformer, said auxiliary path including means for establishing a reverse unidirectional potential drop across said asymmetric unit idr opposing the iiow of said load current through the asymmetric unit, a source of periodic current connected across said conductors7 and signaling apparatus controlled by current from said transformer.

32. In combination with a pair of conductors, a load adapted to receive current from said conducors, a-main source of unidirectional current, an asymmetric unit, means for connecting said asymmetric unit in series with said main source across said vconductors in a direction to aid the ow or current from said main source to said load, an auxiliary source of unidirectional current connected across said asymmetric unit in a direction to oppose the flow oi current from said main source through said asymmetric unit, a source or periodic current connected across said conductors, and signaling apparatus connected in series with said auxiliary'source across said'asymmetric unit and responsive to the :dow of current from said periodic source at such time as the potential drop in said apparatus due to current from said propulsion source and said periodic source is insufficient to overcome the opposing potential of said ,adapted to receive current from said conductors,

E iii an asymmetric unit, means for connecting said asymmetric unit in series with said main source across said conductors in a, direction to aid the flow of current from said main source to said load,

an auxiliary source of unidirectional current co'nnected across said asymmetric unit in a direction to oppose the flow of current from said main source through said asymmetric unit, means for impressing mriodicaily varying signaling energy accesos RALPHOVERHOLT, Jn. 

